Electrical circuit for radioreceivers



1933- s. BALLANTINE 1,930,672

ELECTRICAL CIRCUIT FOR RADIORECEIVERS Original Filed June 17, 1924 IJwue n rot Patented Get. 17, 1933 UNITED STATES ELECTRICAL CIRCUIT FORRADIO- RECEIVERS Stuart Ballantine, Mountain Lakes, N. J., as-

signor, by mesne assignments, to Radio Corporation of America, porationof Delaware New York, N. Y., a cor- Original application :June 1'7,1924, Serial No. 720,708, patented June3, 1930, No. 1,760,871. Dividedand this application December. 21, 1927. Serial No.-241,64=7

14 Claims.

electrical circuits adapted to reduce or suppress the undesired effectsdue to capacity existing between the anode and the control electrode ofa vacuum tube employed in an electrical repeater or amplifier circuit,stage, or the like. intended to accomplish'this result have heretoforebeen known and used. One such circuit is now generally knowncommercially as a neutralized circuit, and comprises, broadly speaking,a capacity and an inductance connected in series between the input andoutput circuits of a vacuum tube stage, the inductance being closelycoupled (i. c. with substantially unity coupling) to a coil in one ofthese circuits and the capacity being connected to an electrode of theother circuit. I have found that circuits of this type, and similarcircuits, as hereafter specifically described, while generallysatisfactory, are subject to certain imperfections in operation. Forexample, experiments with such circuits lead to the conclusion that, sofar as I am aware, they have never, before my invention, been soconstructed and adjusted as to be even approximately unidirectional inaction, 1. e. so as to give approximately true theoretical repeateramplification. Although such circuits may be otherwise perfectlybalanced, a proper control of the resistance balance has not beenobtained prior to my invention. The absence of a proper resistancebalance, or of a proper control of the degree of resistance unbalance,may very considerably decrease the actually-obtained amplification. In atypical specific case of a single amplifier stage of the neutralizedtype, I found that the amplification was less than the theoreticalamount, so that the stage gave only about 85%-90% of the amplificationwhich it would give if it were substantially unidirectional in action,i. e. if it gave its true theoretical repeater amplification. When,however, a proper resistance balance, according to my invention, wasobtained (in addition to the usual capacity balance) this amplifierstage was found to give .its true theoretical repeater amplificationWithin less than one percent.

Referring now to the drawing, Fig. 1 is a circuit diagram showing anaudion or vacuum tube amplifier stage arranged according to myinvention, the circuit being provided with arrangements for rendering itsubstantially unidirectional in action; Fig. 2 is a circuit diagramshowing an am- Circuits plifier stage arranged according to anothermodification of my invention.

Figure 1 illustrates a repeater unit in which the audion capacitycoupling is eliminated by a neutralization method. The principle. oisuchmethods is disclosed in my copending applications, Ser. No. 629,702,filed April 3, 1923 and Ser. No. 167,701, filed Feb. 12, 1927. L1 and L2constitute the input transformer whichis tuned by the condenser C2; C0is a compensating condenser; L3. and L; are either separate coils orparts of the same coil; L5 and C3 represent the output circuit; RC is acompensating resistance; R is a resistance in the filament circuit, thedirect current drop across which is used to give the grid a suitablenegative bias; the C battery reinforces the biasing effect of R; the Aand B batteries have their conventional circuit locations; C1 is afilament-shunting condenser of low impedance. The output circuit,represented by the coil L5, must be'coupled to L3 and Li so that theeffectiveimpedances between the terminals of L3 and L4. are of propervalue to maintain a state of balance in the circuit; obviously also thecoupling between L3, L4

and L5 must be fixed. It is not necessary that L3 and L4 be coupledtogether, but their couplings to L5 must result in irnpedances betweentheir terminals which satisfy the requirements of neutralization. Forbest results, with tubes of the usual 15,000 ohms plate resistance, asnew constructed, the coils L3 and Li are of small inductance comparedwith that of L5 and the coupling between L3 and'Ls and between L4 and L5should be close. In order that persons skilled in the art may reproducemy results, 1 give the following constants of one specific circuit:L3:20 microhenries; L4: microhenries; L5:300 microhenries; C3: 0.00033inicrofarads; Cc=0.000005 microfarads. These values were found suitablefor a unit designed to cover a wave length range of 200 to 600 meters.

Figure 2 illustrates a repeater unit-in which an alternative method ofneutralizing the audion capacity coupling is employed. This method isdisclosed in my copending applications above referred to, and insubstance in liazeltine U. S. Patent 1,489,228, April 1, 1924. The otherarrangements for eliminating the enumerated ecuplings other than thatdue to the audion capacity, are those already described. L1 and L2 aretwo coils of preferably tight coupling wound in opposite directions andso connected that their noncommon terminal voltages are Opposite inphase; Co is a compensating condenser; R1 and R2 are compensatingresistances, which make up the herein described, and equivalentarrangements thereof, fall obviously within the scope of my invention.For example, arrangements in which the compensating or phase-adjustingresistances are wholly or partially embodied in one or more elements ofthe compensating circuit, as the compensating inductance or capacity,are contemplated by me, and fall within my invention. Moreover, myinvention extends to the control of the resistance balance of thecircuit in either direction, and is not limited to a circuit which isperfectly balanced.

I claim:

1. An electrical amplifier circuit comprising, in combination, a vacuumtube including at least an anode, a cathode and a control electrode; aninput circuit connected between said cathode and said control electrode;an output circuit connected between said cathode and said anode andincluding an output transformer; and a compensating circuit including acoil arranged in inductive relation to a winding of said outputtransformer and having one terminal connected to said cathode, andcapacity and resistance connected in' series between the other terminalof said coil and said control electrode.

- 2. An electrical amplifier circuit comprising, in

I combination, a vacuum tube including at least an anode, a cathode anda control electrode; an input circuit connected to said cathode and saidcontrol electrode; an output circuit including an output transformerhaving primary and secondary windings; and a series compensating circuitconnected between said control electrode and said cathode and includinga resistance, a capacity, and an inductance, said inductance beingconnected to the cathode terminal of said output transformer primary buthaving substantially zero electromagnetic coupling with said primarywinding.

3. An electrical amplifier circuit comprising, in

combination, a vacuum tube including at least an anode, a cathode, and'acontrol electrode; an input circuit connected between said cathode andsaid control electrode; an output circuit connected between said cathodeand said anode and including an output transformer having primary andsecondary windings; and a compensating circuit including a compensatingcoil wound in the opposite direction to the primary of said outputtransformer and coupled thereto so that the noncommon terminal voltagesof said compensating coil and of said transformer primary aresubstantially opposite in phase, said compensating coil having oneterminal connected to said cathode and having its other terminalconnected through a resistance and a capacity, in series, to saidcontrol electrode.

4. An electrical amplifier circuit comprising, in combination, a vacuumtube including at least an anode, a cathode, and a control electrode; aninput circuit connected between said cathode and said control electrode;an output circuit connected between said cathode and said anode andincluding an output transformer having primary and secondary windings;and a compensating circuit including a compensating coil wound in theopposite direction to the primary of said output transformer and tightlycoupled thereto so that the non-common terminal voltages of saidcompensating coil and of said transformer primary are substantiallyopposite in phase, said compensating coil having one terminal connectedto said cathode and having its other terminal connected through aresistance and a capacity, in series, to said control electrode.

5. An electrical amplifier circuit comprising a vacuum tube having atleast an anode, a cathode and a control electrode; an electrical networkassociated with said tube and including a counter feedback path aroundthe tube for producing a substantial reactance balance or" said networkas regards disturbing feedback through the capacities of said tube andassociated connections; and means associated with said counter-feedbackpath for controlling the resistance balance of said network.

6. In a radio receiver, an ionic repeater having resonant grid and platecircuits and a coupling between said circuits for establishing a currentto oppose retroactive currents through the capacity between the grid andplate terminals of said repeater, said coupling including a resistanceoperative :to bring the opposing current to the proper phase.

7 An electrical amplifier comprising a vacuum tube, an input circuit andan output circuit having capacitive-coupling between them, acompensating circuit for establishing currents to oppose retroactivecurrents flowing through said capacitive coupling, and means operativeto bring the opposing currents into phase with the retroactive currents.

8. An' electrical amplifier stage comprising a vacuum tube, an inputcircuit, an output circuit, a circuit for compensating the undesirableeffects of coupling between said output and input circuits, and aresistance associated with saidcompensating circuit'for adjusting thephase of the compensating current. v

9. An electrical amplifier stage comprising a. vacuum tube having atleast a plate, a cathode, and a control grid, and having capacitybetween said plate and control grid; an impedance having one terminalconnected to said plate; a connection from an intermediate point in saidimpedance to said cathode, the two portions into which said impedance isdivided by said connection to the cathode having negligibleelectromagnetic coupling with each other; capacity connected between theother terminal of said impedance and said grid; an input circuit forsaid amplifier stage associated with said grid and cathode; and anoutput circuit for said amplifier stage arranged across said impedance.

1 0. .An electrical amplifier stage comprising a vacuum tube having atleast a plate, a cathode, and a control grid, and having capacitybetween said plate'and control grid; an inductance having one terminalconnected to said plate; a connection from an intermediate point of saidinductance to said cathode, the two portions into which the saidinductance is divided by said connection to the cathode havingnegligible electromagnetic coupling with each other; a capacityconnected between the other terminal of said inductance and said grid;an input circuit for said amplifier stage associated with said grid andcathode; and an output circuit for said amplifier stage arranged acrosssaid inductance.

11. An electrical amplifier comprising a vacuum tube, an input circuitand an output circuit having capacitive coupling between them, acompensating circuit for establishing currents to oppose retroactivecurrents fiowing through said capacitive coupling, and resistive meansoperative to bring the opposing currents into phase with the retroactivecurrents.

12. An electrical amplifier comprising a vacuum tube, an input circuitand an output circuit having capacitive coupling between them, acompensating circuit for establishing currents to oppose retroactivecurrents fiowing through said capacitive coupling, and means in saidcircuit operative to bring the opposing currents into phase with theretroactive currents. Y

13. An electrical amplifier stage comprising a vacuum tube, an inputcircuit, an output circuit,

a circuit for compensating the undesirable effects of coupling betweensaid output and input circuits, and a resistance associated with each ofsaid input and compensating circuits for adjusting the phase of thecompensating current.

14. In combination, an electron discharge tube provided with a controlelectrode circuit and an anode circuit, means for tuning the firstcircuit, means for neutralizing the capacity coupling between the twosaid circuits comprising a coil between the anode and cathode of thetube, a second coil coupled to the first coil for transmitting energy,an auxiliary coil and a neutralizing condenser connected in seriesbetween the control

